1. Technical Field of the Invention
This invention relates to curing agents for epoxy resins and more particularly to amines of the type heretofore known for use as curing agents for epoxy resins extended, in accordance with the present invention, by the incorporation thereinto of a solid elastomeric polyurethane. The solid elastomeric polyurethane is derived from an essentially difunctional aromatic diisocyanate, a high molecular weight isocyanate reactive polyether and a difunctional cross linking agent such as a diol or a diamine. The resulting composition is used to cure epoxy resins of the type heretofore known in the art.
2. Prior Art
It is known to use amines such as aliphatic or aromatic amines for the curing of epoxy resins as shown, for example in Waddill U.S. Pat. No. 4,139,524 and Marquis et al. U.S. Pat. No. 4,162,358. See also, the textbook "Handbook of Epoxy Resins" by H. Lee and K. Neville, McGraw Hill Book Co., 1967. There is significant technical literature on this subject as illustrated, for example by a technical brochure entitled "Jeffamine.RTM. Polyoxypropyleneamines", Copyright 1978 by Jefferson Chemical Company, Inc. Becker et al. U.S. Pat. No. 3,847,726 discloses sheet metal laminates wherein the binder is an epoxide formed by curing an epoxy resin with a multi-component curing mixture, one component of which is a Mannich Condensate of polyoxypropylene amine, phenol and formaldehyde.
An extensive body of technical knowledge has arisen relating to the preparation of essentially solid polyurethane elastomers. See, for example, Vols. I and II of "Polyurethane Chemistry and Technology" by James H. Saunders and Kent C. Frish, Interscience Publishers, 1962 and 1964. One such group of elastomers is frequently referred to as RIM polyurethanes. This is an art-recognized term because RIM in an acronym for "Reaction Injection Molding", which is not a material, but rather, a process for molding polyurethanes. In the reaction injection molding (RIM) process two highly reactive streams of chemicals are brought together under high pressure (i.e., 2000 psi) in a small mixing chamber where the streams are impingement mixed by being sprayed directly into each other. The mixed material flows immediately into a warm mold where the chemical reaction is completed and the part is cured. The resultant elastomeric polyurethane will contain small pores and voids so that it is not, technically speaking, a voidless solid material. For example it can be calculated that the theoretical density for a polyurethane elastomer should be about 70 pounds per cubic foot. Normally, RIM elastomers based upon polyurethanes will have a density in the order of magnitude of about 60 pounds per cubic foot. The RIM process and the raw materials used therein are described in greater detail in the text, "Reaction Injection Molding" edited by Walter E. Becker, Van Nostrand Reinhold publishers, 1979.
In reaction injection molding, one of the two streams referred to above is the essentially difunctional aromatic diisocyanate stream.
The other stream is a stream containing a high molecular weight isocyanate reactive polyether based on propylene oxide, a cross linker such as a diol or a diamine and other conventional additives.
A representative list of U.S. patents directed to the preparation of RIM-polyurethanes includes, for example McDaniel et al. U.S. Pat. No. 4,243,760, Dominguez et al. U.S. Pat. No. 4,254,069, Dominguez U.S. Pat. No. 4,273,884, Dominguez et al. U.S. Pat. No. 4,273,885, Gilbert et al. U.S. Pat. No. 4,297,444, Cuscurida et al. U.S. Pat. No. 4,301,110, Cuscurida et al. U.S. Pat. No. 4,309,532, Dominguez et al. U.S. Pat. No. 4,350,778, and McEntire et al. U.S. Pat. No. 4,359,540. Also, Cuscurida et al. U.S. Pat. No. 4,358,547 and Dominguez et al. U.S. Pat. No. 4,362,824.
Solid elastomeric polyurethanes such as RIM polyurethanes are normally used as utilitarian articles such as body parts for automobiles, etc. The resultant scrap and defective moldings present a serious disposal problem. For example an article "The Reclamation of Flexible Polyurethane Foam" found in the Polymer-Plas. Technol. Eng., 19(1), 1-20 (1982), discloses various techniques that have been conceived insofar as the reclamation of highly porous, low density flexible polyurethane foam is concerned. Reclamation of high density polyurethane elastomers presents special problems because of the strength and durability of the materials involved.
Among the techniques for reclamation mentioned in this article is the use of a glycol or an amine as a solvent. As another example, in Lidy et al. U.S. Pat. No. 4,267,078, a process for disposing of scrap polyurethane is disclosed which involves comminuting the polyurethane and reacting it with an alkylene oxide to form a product that can be used to form additional foamed polyurethane. British specification No. 1,595,431 discloses a method wherein a polyurethane is comminuted, melted and then molded into elastomeric polyurethane products such as shoe soles. U.K. patent application No. 2,062,660A is directed to a reclaiming method wherein the polyurethane is heated in the presence of a compound capable of generating ammonia gas on decomposition in order to provide a degradation product.